Air dryers are generally utilized to remove water vapor typically from compressed air or gas. Where refrigerant-type air dryers are employed, a refrigerant system is used to lower the temperature of the air or gas being dried to a temperature at or below the condensation temperature of water therein. At such temperatures, water vapor in the undried air condenses on a surface within a condenser where it can be collected and purged from the system.
In order to sufficiently lower the temperature of the undried air or gas, many refrigerant systems comprise a heat exchanger where heat is drawn from the air or gas being dried to a refrigerant. Typically, heat from undried air is coupled to the evaporation of a colder refrigerant in an evaporator. In this case, as the liquid refrigerant is vaporized, it removes heat from the undried air or gas and cools the air in the process. When the air or gas reaches a temperature at or below the condensation temperature of water therein, the net result is that the water vapor therein begins to condense (or separate) from the air or gas and is collected in a condenser or separator.
In order to recycle the refrigerant in the system, a compressor and a chiller unit are often installed—the compressor compresses the gaseous refrigerant that has been vaporized in the chiller, and the condenser condenses the gaseous refrigerant into a high pressure liquid. The refrigerant is then ready for another cycle of vaporization.
A common problem with refrigeration-type dryers is determining how to suspend cooling (i.e., “de-energize” the system) during times of no load or low load conditions. For example, the demand for refrigeration is low or non-existent when little to no air is flowing through the refrigerator dryer or when the incoming air is already cool. Typically, it is desirable to reduce or discontinue cooling during such periods to avoid ice formation in the refrigerant system that could affect operation of the refrigeration air dryer. Ice can plug the system so that it does not continue drying the air, or it can plug the air passages stopping the flow of compressed air.
One way to prevent excessive cooling and the resulting problem, is to use a cycling-type refrigeration dryer. In a cycling refrigeration-type dryer system, a thermostatic temperature device causes de-energizing of a refrigerant compressor when the undried air has been cooled to a predetermined temperature. This can also be accomplished by measuring the evaporator pressure. The same device can then cause the compressor to be re-energized when the temperature in the evaporator elevates to a predetermined temperature, indicating further cooling is required to remove moisture from the incoming air. Thus, it has been found that between adequate load and low load conditions, a refrigeration compressor may cycle on and off about thirty to forty times per hour.
The number of cycles per hour is significant because frequent cycling adds costs associated with wear and tear on the compressor, control systems, and valves. As a result, the life without maintenance of the refrigeration system is drastically reduced. Accordingly, it would be desirable to provide a refrigerant air dryer system and method that extends the life of its refrigeration system.
Moreover, the greater the number of times a refrigeration system cycles, the greater the amount of energy that is consumed. Lower energy consumption has both cost and environmental benefits. Accordingly it would also be desirable to provide a refrigeration dryer system and method that reduces the amount of energy consumed.